1. Field of the Invention
This invention relates to a process for preparing a vinyl chloride polymer, particularly to a process for preparing a vinyl chloride polymer which has a high bulk density, and yet can be processed to give a molded or formed product having a small number of fish eyes.
2. Description of the Prior Art
Vinyl chloride polymer is a useful resin having excellent physical properties, and is utilized widely as rigid materials and soft materials. As the method of processing such vinyl chloride polymer, such methods as calendering, extrusion, injection molding, etc. are generally used. In recent years, in preparation of rigid extrusions, in order to increase the extrusion output of extruders, it is required to develop a vinyl chloride polymer with a high bulk density.
Accordingly, in production of a vinyl chloride polymer by suspension polymerization in an aqueous medium, as the process for obtaining a vinyl chloride polymer with high bulk density, there have been proposed a large number of processes such as the process in which monomer is added in the course of polymerization (Japanese Pre-examination Patent Publication (KOKAI) No. 168008/1984), the process in which a highly saponified vinyl alcohol is used (Japanese Pre-examination Patent Publication (KOKAI) No. 7600/1982), etc.
However, according to the processes described in the above-mentioned Japanese Pre-examination Patent Publication (KOKAI) Nos. 168008/1984 and 7600/1982, although polymers with a bulk density which is high to some extent can be obtained, there is involved the problem that fish eyes are increased in the formed or molded product of the polymer obtained. Also, the bulk density of compositions containing various formulating ingredients added to the polymer obtained is not sufficiently high.